An emergency appropriation is one that the President and the Congress have designated for an emergency requirement under the BEA that cannot wait for the regular budgetary process. If it pertains to a discretionary program, such an appropriation results in an adjustment to the discretionary cap.
Under President Bush and the last several congress Emergency Appropriations Bills have been passed in order to fund the military operations of the Iraq War, Operation Enduring Freedom, Hurricane Katrina Relief and for security issues after September 11th, 2001. However the appropriations have also become stuffed with Porkbarrel projects, ammendments that add billions of dollars but do not specifically relate the bill being passed.
-  The Heritage Foundation : Larding Up Emergency Appropriations